Hot water loop

A while ago there was a lot of information on adding a return line to
your hot water system, insulating the original line, and taking
advantage of gravity to have instant hot water on the second floor. I
had them add such a line when we remodeled our bathroom, and it works
wonderfully. Thanks to those who brought this subject up.
The cork floor in the bathroom is another idea I got here that is
looking really good.

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Our new house comes with this standard and I'm really looking forward
to having it. The master bedroom is as far as it can get from the
water heater and still be in the house, so it should make a big
difference.
I've coveted such a system ever since a friend bought a ca. 1930 house
with it. His was multi-floor and convective, while mine will have a
pump.
Mary

I went and read a bunch of those articles. There were some differing
opinions on whether to use a passive (convection) loop or an active
(pumped) loop. Can you give some details on the length of the run for your
passive system?
I am getting ready to replace all my old galvanized pipe with new copper
and this sounds like a great idea. I have most of the area where the pipes
will run opened up already, so I will just need some extra pipe and
fittings.
Some quick sketching suggests I will use about 65' of extra pipe, and my
total loop will be about 130'. I am planning on 3/4" pipe; one pump
manufacturer site I saw suggested that a 3/4 supply line only needed 1/2"
for the final portion of the loop. What size pipe did you run, and did you
run a smaller size for the final section of the loop?
Did you install a swing gate valve (?) as some people suggested doing,
connecting the return loop via the valve to the cold water inlet, or did
you tap into the heater drain connection?
Can anyone recommend a book or site that discusses the design of
recirculating hot water systems? I have found a few sites, but would like
to make sure my design is correct before I start running pipe.

I think you'll find that this is somewhat of a lost art, and there's relatively
little "hard design" information available. Beyond the obvious of it works
better with more "vertical" systems (stacked kitchens and bathrooms), avoid
dips in lines, slope horizontal runs in the right direction, try to
run your system linearly, etc.
I suggest making a best guess, but factor into your design the possibility
that you may have to insert a recirculating pump on a timer.
Another possibility is the devices that you hook into the hot and cold system
right at the (farthest) fixture. These detect temperature differences between
hot and cold, and pump water from the hot side to the cold side to bring the hot
side up to a reasonable temperature. These can be quite effective if they're
tuned properly.

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Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

I have an old house where the bath is above the kitchen. The hot water
line was 3/4 from the heater to the common wall (about 20 feet), then
half inch to the kitchen, and up the wall to the bath. In retrospect, I
wouldn't use such large pipe in that situation, since it took forever to
run out all that cooled water in the morning. The plumber on the crew
didn't know about looping, but the GC did and suggested running 3/4 from
the bath down the wall, then over to the water heater, insuring that it
was sloped down toward the heater to facilitate circulation. They
hooked up the return to the drain fixture on the water heater with what
I think they called a nipple: an extension of pipe from the heater to
the drain fixture, with a tee for the circulating return. I had asked
for a check valve to insure no backflow, but they forgot it and mine
works well without it, possibly because there is a lot of elevation from
the basement to the bath. I had already put insulation on the supply
line some years ago, and there is none on the return line. The return
line is constantly hot, so I guess I am losing some energy there, but I
am saving water by not having to run it until it warms up, and the
comfort of instant hot water is well worth it.
My brother-in-law had a newer home, with a circulating system built in.
In that, all the lines were insulated, but they had pumps to circulate
the water.

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Plumb it into the water heater's drain with a T and a nipple. (Those plastic
valves the new heaters come with I wouldn't trust anyway.) You may or may not
ever need a pump. Natural convection tends to do the job of circulating the
water for you, but plan for a pump should the need arise. I used a check valve.
There was 1 spot under my 2nd floor hall (about 36") where I could not insulate
the return line. So there's always a warm spot there, and 9 times out of 10,
one of the cats is taking a nap on it.

I wouldn't use the drain. You need that for other reasons.
T'ing it into the supply line _should_ work, but you will NEED a
check valve on the return line, otherwise, you may not be able to get
much hot water at the other end.

--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

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